Retaining walls for use in various landscaping projects are available in a wide variety of styles. Numerous methods and materials exist for the construction of retaining walls. Such methods include the use of natural stone, poured in place concrete, pre-cast panels, masonry, and landscape timbers or railroad ties.
In recent years, segmental concrete retaining wall units which are dry stacked (i.e. built without the use of mortar) have become a widely accepted product for the construction of retaining walls. An example of such a product is described in U.S. Pat. No. Re. 34,314 issued to Forsberg (Forsberg '314). Such products have gained popularity because they are mass produced, and thus relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install, and couple the durability of concrete with the attractiveness of various architectural finishes. The retaining wall system described in Forsberg'314 has been particularly successful because of its use of a block design that includes, among other design elements, a unique pinning system that interlocks and aligns the retaining wall units, allowing structural strength and efficient rates of installation. This system is advantageous in the construction of larger walls when combined with the use of geogrids hooked over the pins, as described in U.S. Pat. No. 4,914.876 to Forsberg.
An important consideration in the design of retaining walls is their aesthetic appeal. Retaining walls (especially larger retaining walls) may present a rather monolithic and monotonous appearance. One way of enhancing the visual appearance of a wall is to integrate plantable spaces within the wall which can hold and sustain plant life. On larger walls, providing plantable space within the wall can break up the appearance of monolithic concrete. On smaller walls, such as those used in residential applications, appearance may also be improved by adding plants. Therefore, the ability to integrate plant life into a structurally sound retaining wall offers considerable aesthetic benefits.
Several approaches have been used in the past to construct a retaining wall incorporating plantable space, but each has had shortcomings. One approach has been to construct the wall with standard retaining wall blocks built so that it has one or more terraces. Although terraced walls allow the terraces to be planted, they have several disadvantages. First, the plantable area is confined only to the horizontal terraces. Thus, only limited portions of the wall structure can be enhanced with plantings, which limits design flexibility. Additionally, many wall designers desire to intersperse plantings throughout a wall's surface in order to create a "green" wall, i.e. a wall whose structural members are effectively concealed by the plantings. A second disadvantage of using terraces is that they take more space than a wall without terracing. In certain circumstances, as where a wall runs along or near a property line, or where limited space is available or affordable for other reasons, a terrace may not be feasible. Under any circumstances, the terrace will diminish the mount of usable space on a site and thus may lower the site's real estate value. Third, walls built with terraces are more difficult to engineer and to build than are walls without terraces. Particularly where the upper tiers of the wall are located relatively close behind the lower tier or tiers, the upper tiers place additional loads on the lower tier or tiers. Moreover, tiered structures raise global stability issues not present with respect to single walls and are prone to settlement. Finally, on taller walls the terraces may not be accessible and may be difficult or dangerous to maintain to prevent growth of undesired plant life.
A second approach to constructing plantable retaining walls has been to use specialized retaining wall units designed to accommodate planting. This method relies on two principle design features, either singly or in combination, to allow planting to be incorporated within the wall. The first feature is to increase the amount of setback between courses or rows of blocks to allow access to a soil retaining cavity in which plants can be grown. The second is to construct the wall with spaces between horizontally adjacent blocks which allows the soil behind the wall to be accessed for planting. For purposes of clarity each of these features will be discussed individually.
The first design feature relies on the amount of setback between courses or rows of blocks to allow construction of a plantable wall. The setback of the wall is the amount that the wall leans back into the retained earth. Segmental retaining wall units are commonly designed so that the blocks can readily be installed with a predetermined amount of setback per course. For a non-plantable segmental retaining wall unit, setbacks ranging from zero degrees (i.e. no setback) to approximately 12 degrees are common. With a plantable unit, this setback is generally much greater and can be as much or more than 51/2 inches per 8 inch course. The setback is typically combined with the use of a plantable cavity in the blocks. Since the setback from course to course is as much as 51/2 inches, ample space in the plantable cavity in each block is exposed to allow for planting. There are, however, numerous disadvantages in relying on setback to allow planting in a retaining wall. The use of setback to allow planting is similar to the use of terraces. The higher the degree of setback, the greater the amount of land area needed to accommodate the retaining wall structure. Additionally, setback retaining walls create both aesthetic and functional problems for the wall especially when curves or comers are built. Because the units are setback, when an outside curve is built, the units will bind as succeeding courses are laid. This necessitates cutting individual blocks to fit. If an inside curve is built the units will gap apart as the wall is built up. Thus, units with significant amounts of setback are truly suitable only for straight walls. Finally, walls with a high degree of setback also raise global stability issues and may be more expensive to build and engineer than walls with less setback.
The second design feature used in constructing plantable segmental retaining walls is to provide horizontal gaps in the wall structure. This is typically accomplished by leaving spaces between the units or blocks of each course. This approach is frequently incorporated along with the use of setback. With or with out setback this approach suffers several defects. Such an approach compromises the retaining wall's structural soundness. Since gaps are left in the structure, the structure is prone to suffer the effects of either gradual or catastrophic events of erosion. The gapping of the units results in point loading on the units, which can cause cracking or other structural weaknesses. In addition, such systems are not suitable for larger structural wall use because the gapping weakens the wall's ability to withstand significant earth pressures. Finally, walls built in this fashion are not as easy to install because the amount of gapping is typically not predetermined by the unit's design and must be adjusted based upon "eye-bailing" unit placement, or taking the time to measure the position for each block as it is placed. This may result in haphazard placement of the units or inefficient rates of production in the installation of the wall.
In view of the various disadvantages which exist with respect to the construction of conventional plantable retaining wall units, there is a need for a plantable retaining wall block and retaining wall constructed from the block which overcomes these disadvantages. Specifically, it would be desirable to provide a plantable wall block which allows the construction of retaining walls of varying degrees of setback using one basic retaining wall block which has alignment means which allow the wall builder to choose among multiple setback options. It would also be desirable to provide a plantable retaining wall block that integrates effectively with standard non-plantable retaining wall blocks, including matching the degree of setback used by the standard retaining wall blocks and the connection system of the standard blocks.
Accordingly, it is an object of the present invention to provide a retaining wall block that is constructed with a plantable area that is capable of being built into structurally sound, vertical or minimally setback walls while providing adequate space in the wall to insert soil and plant material, and to allow plant growth.
Another object of the present invention is to provide a retaining wall block that is constructed with a plantable area that provides the wall builder with multiple alignment guides to permit the efficient construction of plantable retaining walls with predetermined amounts of setback.
Another object of the present invention is to provide a retaining wall block that is constructed with a plantable area that, when laid in a running pattern, creates horizontal spaces for planting of the course below, without creating any gaps in the retaining wall structure, and which may be laid in a manner which results in the construction of a vertical wall or wall with minimal setback.
Another object of the present invention is to provide a plantable retaining wall block with minimal setback that uses interlocking means that do not require the use of a separate pin or spacing device.